A need has existed for a long period of time for a more reliable electrical igniter for liquid propellants. In the past, liquid propellant igniter systems included the use of electrically driven hot wire, exploding wire and spark and arc electrical discharges for the relatively low energy systems. The high energy and high power prior are igniters used electrically initiated plasma torch and plasma cartridge devices.
Prior art electrical igniter devices for liquid propellants frequently used a small diameter central pin type electrode surrounded by a larger diameter tube as the second electrode. In most cases the central electrode is shorter in length than the outer cylindrical electrode. The inside region of the outer cylinder is typically filled with a liquid propellant, surrounding and covering the central electrode. The output end of the outer tube of the igniter is usually of a somewhat reduced diameter to provide a small to moderate restriction of the liquid propellant and hot combustion gases flowing out of the igniter housing. Ignition occurs when a spark or arc discharge flows through the liquid propellant for sufficient time to initiate a self-sustained burn of the liquid propellant. It is during this initiation period that the restriction in output flow from the igniter causes the pressure within the igniter to increase and improve the ability to cause self-sustaining and reproducible ignition.
One of the problems with the aforedescribed prior art devices has been achieving high pressure seals between the electrode elements and the supporting high strength metal and insulator structure igniters.
Another problem of the prior art is maintaining the durability of the electrodes. After repeated ignitions the electrodes are eroded by the arc discharge and by the high temperature gases generated by the liquid propellant combustion. Changes in electrode shape and spacings frequently reduced the reliability of ignition of the prior art devices.